It is commonly accepted that language functions are processed asymmetrically in the human brain, with the left hemisphere dominant. It is believed that this lateralization enables the rapid perception, organization, and production of the complex acoustic signals that are essential for human spoken language. For those interested in the evolution of both the behavioral and neurological substrates of human speech, it is imperative to examine the phylogenetic origins of this neural lateralization. One way to approach this issue is to study the neuroanatomical structures involved in the perception and processing of nonhuman primate vocal signals. Advances in functional neural imaging techniques now make it possible to examine these systems in vivo. The following project is proposed to determine whether or not chimpanzees, Pan troglodytes, perceive and process communicatively salient vocalizations via a left- lateralized mechanism. To accomplish this aim, Positron Emission Tomography (PET) will be used to visualize neuronal activity in chimpanzees while perceiving conspecific vocalizations. [unreadable] [unreadable] [unreadable]